1. Field of the Invention
The present invention relates to bone conduction audio communication systems and, more particularly, to bone conduction audio speakers and microphones.
2. Description of the Related Art
Most conventional audio listening and/or communication systems do not use bone conduction. Instead, such conventional systems provide sound to the listener utilizing normal air conduction via the ear canal. Such conventional systems are used in a variety of applications or activities. One type of well known air conduction system is the headphone or earphone that is placed over the ear and transmits sound to the user via the ear canal. As well, conventional microphones utilize air vibration transducers to translate incoming air movement (sound/audio) into electrical pulses.
In contrast, it is also known to provide bone conduction microphones that utilize energy generated by auditory vibrations of the bones of the head. Generally, these types of microphones utilize an inertial-type or low mass accelerometer transducer which is placed in intimate contact with the head to detect bone vibrations and then generate output signals responsive to the vibrations.
However, these types of microphones are adversely affected by ambient noise transmitted through the air as well as through mounting equipment. Also, the audio quality is generally poor because the transducer cannot be held in intimate contact with the head with a sufficient, but comfortable, pressure so as to pick up or detect all frequencies of sound, especially high frequencies.
What is therefore needed in the art is a bone conduction audio communication system having both a microphone and speaker that overcomes the deficiencies of the prior art.
The present invention provides a bone conduction microphone and speaker which comprise separately and together a communication system. Both the speaker and microphone are designed to be in contact with the head, head area, or on the mastoid of a user.
The present microphone is constructed with materials and geometries such that the acoustic impedance thereof is nearly matched to the human skull structure. Additionally, the present microphone is designed to create the largest possible acoustic mismatch with air, attenuating ambient air coupled sound by greater than 80 dB, thereby almost completely eliminating air coupled sound reception. Further, the present microphone is specific to vibrations which exist in the human flesh and is specifically not sensitive to ambient air coupled vibrations, while at the same time being constructed with simple and inexpensive components.
In one form thereof, the microphone comprises an audio transducer potted within a low profile plastic housing and including a transistor and resistor mounted directly to the audio transducer.
The audio transducer is preferably a piezoelectric ceramic bender having a ceramic element disposed on a metallic vibration element and of appropriate operating characteristics. A Junction Field Effect Transistor (JFET) has the gate thereof electrically coupled to the ceramic element, the source thereof electrically coupled to the metallic vibration element, and the drain electrically coupled to the output conductor. The resistor has one end electrically coupled to the ceramic element and the other end coupled to the metallic vibration element.
The present speaker is a bone conduction transduction device with acoustic impedance matched for bone conduction sound. The speaker is placed in intimate contact with the head or head area of the user such that sound generated thereby is injected directly into the skull creating a minimum of ambient air excitation.
In one form thereof, the present speaker comprises an audio transducer and audio transducer potted within a plastic housing. The audio transducer is supported on a foam layer disposed between the audio transducer and audio transformer. Depending on the application, the audio transducer may also be supported on a shelf of the housing.
The audio transducer is preferably a piezoelectric ceramic bender having a ceramic element disposed onto a metallic vibration element and of appropriate operating characteristics. The ceramic element is preferably disposed adjacent a protective polyurethane layer.
In another form thereof, the present speaker comprises an audio transducer potted within a plastic housing and disposed adjacent a foam layer, and electrically coupled via a cable to an audio transducer potted within a separate plastic housing. The audio transducer is supported on a foam layer disposed between the audio transducer and audio transformer. Depending on the application, the audio transducer may also be supported on a shelf of the housing.
It is an advantage of the present invention that the specific microphone and speaker designs can be independent of the application.